Prior to my invention, objectionable repeating patterns were limited by the use of strip shingles of two or more different shapes on the same roof. The strip shingles were of complementary shapes, as in U.S. Pat. No. 3,407,556, or there were two pairs of complementary shapes, as in FIGS. 1-4 of U.S. Pat. No. 2,171,010, wherein the tabs on a "right" and a "left" shingle of each pair were arranged in reverse order from each other with respect to the different widths of the tabs, at least some of the tabs on a "right" shingle of one pair had different lengths from corresponding tabs on a "right" shingle of the other pair, and at least some of the tabs on a "left" shingle of one pair had different lengths from corresponding tabs on a "left" shingle of the other pair, which resulted in shingles of four different shapes. Alternatively, shingles of two different non-complementary shapes were used, as in FIGS. 5-7 of the latter patent, wherein the different tab widths of one shingle correspond to the tab widths of the other shingle, but the order of the tabs on one shingle was scrambled from the order of the tabs on the other shingle, rather than being merely reversed as in shingles of complementary shapes. Shingles of different shapes complicated manufacturing, packaging, storing, and shipping and confused roofers.
Objectionable repeating patterns were also limited by using shingles of the same shape, but applying them with irregular offsets between shingles of adjacent courses. The specifying of irregular offsets confused roofers.